This invention relates to an economical, continuous, integrated process for preparation of lithium hydroxide monohydrate and high purity lithium carbonate of large average particle size from a relatively impure lithium carbonate feed.
Recent advances in the glass and ceramic industry have created a demand for higher purity raw materials. For example, technical grade lithium carbonate has not proven entirely satisfactory for use in the production of some specialty glass compositions. In addition, in recent years lithium carbonate has begun to be used in the treatment of manic depression. These diverse uses have created a demand for high purity lithium carbonate, which compound should also have a large average particle size to be acceptable for use in the ceramic and glass industries.
By the expressions "high purity" and "large average particle size" as used in this specification and appended claims is meant that the lithium carbonate has a chemical analysis showing a lithium carbonate content of at least 99.3%, and not more than 0.015% calcium, 0.013% sulfate ions, and 0.01% sodium; and that the particle size is such that at least 50% of the particles are plus 140 mesh, respectively. Typically the high purity Li.sub.2 CO.sub.3 products obtainable by the present invention may contain as little as 0.006% Ca, 0.010% SO.sub.4, and 0.002 Na.
It is known that such a lithium carbonate product can be obtained from dilute solutions of lithium hydroxide through precipitation with carbon dioxide. However, the production of lithium carbonate using such dilute solutions has been found to be uneconomical since the yield is only about 65%. In addition, if the lithium carbonate is produced by reacting carbon dioxide with a solution formed from highly pure lithium hydroxide, the use of this relatively expensive starting material inordinately increases process costs.